"I don't know who you think I am, but let me remind you all. I'm the son of the Demon King, and the first of Son's greatest rivals! And there's no chance that I would stand by while the Saiyans are the only ones to gain strength." Piccolo ~ The Namekian God
Mystic Kaioken (Shinju Kaioken) - a technique developed by Piccolo, during his training under Whis to master god ki. This technique was developed in response to Beerus' awakening, as well as the Saiyans Goku and Vegeta, obtaining the Super Saiyan God and Super Saiyan God Super Saiyan (Super Saiyan Blue) transformations.
After the events of Freeza's Resurrection, the battle against Goku Black and Zamasu, as well as his performance in the tournament with Universe 6, Piccolo comes to the realization that his current power is insufficient against the level of threats facing not just the Earth, but Universe 7 itself. Not willing to rely on the powers of Goku and Vegeta, Piccolo approaches Whis and requests training in learning and mastering god ki. Out of mere curiosity, Whis accepts, quickly discovering that his newest student is a meticulous learner, as the Namekian strives to master all aspects of using god ki. Piccolo is quickly able to do so, and during his training, considers the possibility of further strengthening such ki.
Whis' curiosity is peaked, and questions how the Namekian intends to do so, and Piccolo reveals his own mastery of the Kaioken technique. Whis recognizes it instantly from having witnessed Goku, along with the Human Z-fighters, use the technique at various stages. The angel encourages Piccolo to attempt utilizing his newly acquired god ki with the Kaioken, and after several instances of trial and error, the Namekian is able to gain a handle on this new technique. The result is a massive boost in Piccolo's already considerable strength, with Whis remarking that it's initial power is very similar to that of Goku and Vegeta's Super Saiyan God form. Unsatisfied with just that, Piccolo chooses to continue focusing on gaining an even greater grasp on the combination.
Whis suggests having Piccolo use the technique in sparring, and Piccolo worriedly believes that the angel is suggesting a spar with Beerus. However, Whis calms Piccolo by claiming that he will spar with the Namekian instead, stating that it will be beneficial to Piccolo not only by enabling him to gain practical experience with using the new technique, but also will allow Whis to observe Piccolo's fighting skills and make suggestions for improvement. After a few moments of contemplation, Piccolo accepts, noting that having the assessment of an angel is too good of an opportunity to pass on. Days later, Piccolo opts to return to Earth, with both he and Whis agreeing that the Namekian has thoroughly achieved his objective.
Piccolo returns to Earth, only to learn that Goku has gone to remind Zeno of the Tournament of Power. Frustrated with the Saiyan's battle lust, Piccolo opts to go see Gohan, offering to personally train his former student to prepare for the tournament. Gohan accepts, mainly out of wanting to see his mentor's new strength, and the young Saiyan meets with his mentor at the Room of Spirit & Time, where Piccolo advises that he take the training seriously from the very start. Having realized that his power had dropped considerably during the battle with Freeza, due to having not trained for a few years after Buu, Gohan reveals that he had spent time training in the gravity chamber, alongside Yamcha and Krillin (with Tenshinhan having been too occupied with running the new Crane school). Confident in his strength, Gohan initially ignores the Namekian's advice, believing that having recovered the strength he'd lost would be enough to give his mentor a workout, the Saiyan is easily and quickly overwhelmed by Piccolo's new strength.
Realizing his mentor's suggestion was correct, Gohan powers up to his fullest, with the two beginning their training. Over the span of 24 hours, Piccolo instructs his former charge in acquiring god ki, telling the younger Saiyan that if it were possible for Vegeta to obtain the Super Saiyan God, and later Super Saiyan God Super Saiyan forms, without the need for the Saiyan ritual, then he is confident Gohan could also achieve such strength. Gohan initially isn't interested in achieving those forms, wanting to rely on his own strength. In response, the Namekian goes a step further, revealing both variations of the Mystic Kaioken technique, displaying what he was able to accomplish solely through mastering god ki. Gohan is astonished at the depth of his mentor's level of strength, and at Piccolo's encouragement, the young Saiyan dedicates himself to learning the ability as well. The results of which are seen when Goku arrives with a newly recruited Android #17.
Realizing the two had been training, Goku quickly suggests a tag team spar between himself and #17 against Gohan and Piccolo. As Father and son battle, Piccolo remarks that now would be an opportune moment to settle the fight from all those years ago. The Android agrees, and the two begin battle, with the Android initially gaining the upper hand after a few minutes. Piccolo compliments the Androids' growth, with #17 revealing that his years of sparring with the upgraded Android #16 (who now possessed an unlimited energy drive itself) had ensured that he wouldn't lose against the Saiyans. Realizing what the android was suggesting, Piccolo confidently remarks that he no longer needs to hold back, and begins utilizing the Mystic Kaioken, quickly surprising #17 and closing the gap in their strengths. #17 is surprised by this new ability, and remarks with excitement that their fight won't be as boring as he thought it might be. Their fight is left unfinished, however, as the spar between Goku and Gohan ends.
Goku compliments his son's newfound strength, and enthusiastically throws his support behind his son being Universe 7's team leader. Both Piccolo and #17 agree, and Gohan embarrassingly accepts, with both the Namekian and Android agreeing to settle their fight after the tournament's finished. Goku remarks with excitement that not only would he like to see that fight, but that he would eagerly want to face the winner, unsure how a fight with either warrior would end. Both Piccolo and #17 silently acknowledge the strength of the other, and their confidence in the team's ability to win. Later, during the tournament, Piccolo uses both variations against Hit and later Toppo, but is eliminated in a battle with the latter's God of Destruction mode. Impressed by Piccolo's showing, Shin requests the Namekian to teach him and his attendant, Kibito, the technique. Piccolo complies, and eventually both Kaio are capable of utilizing the technique, though their aura differs from that of Piccolo, with Shin becoming able to surpass the power of his former fellow Kaio, the South Supreme Kai.
Usage and Power
The power of Piccolo's Mystic Kaioken technique is very formidable, capable of rivaling that of both the Super Saiyan God and Super Saiyan God Super Saiyan transformations. It's strength is so great, that upon finishing finally learning the technique, Whis remarks that had Piccolo been capable of wielding this power against Goku Black, he would have stood a good chance at beating the rogue Saiyan. According to Piccolo, who had mastered the original Kaioken up to x20, just using the basic variation of the Mystic Kaioken is enough to rival the strength of a Super Saiyan God, and that using the advanced variant is able to compete on the same level as a Super Saiyan God Super Saiyan. However, Piccolo reveals to Gohan that the advanced variant is the highest he is capable of using without overtaxing his body, but states that should the situation require it, he is willing to go beyond that should it be required.
During the Tournament of Power, the display of his full power impresses a number of onlookers, both among the gods of destruction, and the universe's strongest fighters. This is shown when the Supreme Kai of Universe 7, Shin, requests that Piccolo teach him the technique should their universe be victorious. The Grand Minister states that just the basic variant of his technique ranks at an 8 on the God tier scale.